eas ea ee ee ee Pee 
ie penis 2 
aR eT 
1905] SNOW—DEVELOPMENT OF ROOT HAIRS 25 
results: are due prema to the different amounts of water in the 
‘soils used. 
Roots of corn grown in grenited quartz, garden soil, and air gave 
these results: in quartz, av. length 19.5™™, hairs abundant; in soil, 
-22.3™™, hairs good; in air, 50"™, hairs poor. From these figures 
it seems that the resistance of the substratum bears direct relation 
to hair production; but the factor of water supply has undoubtedly 
an important influence, the quartz being less: compact and therefore | 
drier than the garden soil. Other experiments showed slower growth 
in air and quartz than in soil or water. 
The behavior of roots of Elodea in the substratum has been men- 
tioned, with the suggestion that retardation due to the soil particles 
was the principal factor. It will be shown later that a diminution 
of oxygen supply has a tendency to suppress hair production. There 
is less oxygen in the substratum than in the freely flowing water 
above it. It appears, therefore, that retardation, whether from soil 
resistance or chemical influence, must be the chief factor in producing 
the kinking and the hairs. Whether the hairs are due to the kinking, 
or both are due to the retardation of growth, cannot be stated. The 
production of hairs by retarding growth with glass tubes took place 
_at times without kinking, though in the majority of cases the two 
results were associated. SCHWARZ (75, p. 159) considers “‘nutation” 
(kinking) the most potent factor in the production of root hairs, 
but it seems as if they might both be referred to unequal retardation 
of the growth of the root. Measurements of the epidermal cells of 
roots of Elodea give the following averages in millimeters: 
ae “Sie smooth ; | Haired 
WARES ooo ct pol OCTOR ek 
4; 
re ee 0.110 | 0.077 
Ee eae 0.128} 0.065 — 
Here the soil roots:show better hairs than the quartz, and have 
the shortest cells when hairy. As will be seen later, however, the 
comparative lengths of cells of different roots can only be taken as 
supporting not as decisive evidence. 
Corn seedlings were allowed to send their roots between glass 
